The Greater Manchester Police computer network was down for three days this week, due to infection by the Conficker worm.

The worm infected computers at the Greater Manchester Police, forcing officers there to rely on neighbouring jurisdictions to access the national criminal records database, according to published reports.

Rather than run the risk of infecting the rest of the Police National Computer network, the Manchester network was disconnected from it. The worm was brought under control by Monday afternoon, and it was expected that the network would be brought back online sometime yesterday.

Investigators are leaning toward blaming the outbreak on an infected memory stick that someone plugged into a computer on the network.

The Conficker worm, which was discovered in November 2008, continues to morph and spread, with some estimates putting its sphere of influence at 7 million computers.

Despite its size, the botnet it controls has rarely been used and usually not in very large numbers. Some investigators theorise that the author doesn't want to attract even more attention, so is keeping the botnet's activity to a minimum.